Why facing error due to spacing?

[ajiten]

class BinaryTree:
def __init__(self, root):
self.key = root
self.left_child = None
self.right_child = None

def insert_left(self, new_node):
if (self.left_child is None):
self.left_child = BinaryTree (new_node) # face run-time error here?
else:
t = BinaryTree(new_node)
t.left_child = self.left_child
self.left_child = t
def insert_right(self, new_node):
if self.right_child is None:
self.right_child = BinaryTree(new_node)
else:
t = BinaryTree(new_node)
t.right_child = self.right_child
self.right_child = t
def get_right_child(self):
return self.right_child
def get_left_child(self):
return self.left_child
def set_root_val(self, obj):
self.key = obj
def get_root_val(self):
return self.key r